These conditions are called “obstructive” because it’s as though something is blocking the smooth flow of air in and out of the lungs.

Doctors estimate that more than 24 million people in the United States have emphysema or another form of COPD. Many of them don't know it.

How Does It Happen?

You get emphysema when the linings of the tiny air sacs in your lungs become damaged beyond repair. Over time, your lung damage gets worse. Here’s what happens:

The fragile tissues between air sacs are destroyed and air pockets form in the lungs.

Air gets trapped in these pouches of damaged tissue.

The lungs slowly get larger, and you find it harder to breathe.

If you have symptoms of emphysema, your doctor will do tests to see how well your lungs work. If you have the condition, you won’t be able to empty your lungs of air as quickly as you should. Doctors call this “airflow limitation.”

What Are the Causes?

There are two major known causes of emphysema:

Smoking. Most of the time, tobacco is the main culprit. Doctors don’t know exactly how smoking destroys air sac linings, but studies show that smokers are about six times more likely to develop emphysema than are nonsmokers.

Doctors don’t know why some smokers get emphysema and others don’t.

There is no cure for emphysema, but if you’re a smoker with the disease, kicking the habit might help slow down the damage it does to your lungs.

AAT deficiency: Alpha-1 antitrypsin (AAT) is a natural protein that circulates in human blood. Its main function is to keep white blood cells from damaging normal tissues. The body needs these cells to fight infections.

An estimated 100,000 people in the United States were born with a condition that keeps their bodies from making enough AAT. If you have AAT deficiency, your normal white blood cells will damage your lungs. The harm is even worse if you smoke.

Over time, most people with severe AAT deficiency develop emphysema. If you have this disease, you may also develop liver problems.

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Other Possible Causes

Secondhand smoke. Doctors have long known that being around cigarette smoke -- even if you aren’t a smoker -- can lead to lung damage over time. Several studies suggest that people exposed to high amounts of secondhand smoke probably have higher odds of getting emphysema.

Air pollution. Scientists believe this plays a role, but it’s hard to measure. That’s because most people are exposed to pollution, but emphysema takes years to develop.